(1). Field of the Invention
This invention relates to a multilayer element which comprises an ordered alternating arrangement(ABABAB . . . ) of organic and inorganic layers and to a multilayered structure which comprises such an element supported by a substrate. Further, the invention relates to a step-wise adsorption process for the manufacture of such a multilayer element and multilayered structure.
(2). Description of the Prior Art
The production of ultrathin films and multilayered products has long been known. The Langmuir-Blodgett ("LB") method produces such layered products by the sequential transfer of monolayers of organic material from a water surface to a solid substrate. Although the LB process can provide well-ordered, densely packed mono-and multi-layered structures useful for many applications, e.g., nonlinear optics, x-ray, and microelectronics, these products and their use are attendant with certain disadvantages. The layers in the ultrathin layered products of LB are mechanically unstable, being held together primarily by van der Waals forces. Also, the products that can be produced by the LB method are somewhat limited because the organic material for building up the layers must be spreadable on the water surface. Further, these products find somewhat limited utility as the process only allows small substrates to be coated.
Spontaneous self-assembly (SA) of molecular adsorbates onto certain solid substrates can also provide densely packed monolayers, and this technique has been extended in recent past to the formation of multilayers in selected systems. Examples include Guang Cao, Hun-Gi Hong, and Thomas E. Mallouk, Acc. Chem. Res. 25, 420 (1992), "Layered Metal Phosphates and Phosphonates: From Crystals to Monolayers;" N. Tillman, A. Ullman, T. L. Penner, Langmuir 5, 101 (1989); H. Lee, L. J. Kepley, H.-G. Hong, Thomas E. Mallouk, J. Am. Chem. Soc. 110, 618 (1988); S. D. Evans, A. Ulman, K. E. Goppert-Berarducci, L. J. Gerenser, J. Am. Chem. Soc. 113, 5866 (1991). The presence of covalent bonds or ionic attraction between layers in these structures provides additional stability in multilayered structures not seen in those from the LB system; however, in many SA systems, adsorption of ordered multilayers has proven difficult.
U.S. Pat. No. 5,208,111, which issued on May 4, 1993, discloses one- or multilayered elements applied to a support or substrate. The support in this product is first modified so that its surface is provided with ions or ionizable compounds of the same charge. Then, one or more layers of organic materials are applied to the support, each such a layer containing ions of the same charge but next adjacent layers being of an opposite charge. The first such a layer applied to the support has ions of opposite charge to the ions on the support's modified surface. The individual layers are disclosed to be produced by application of a solution of the organic material in a suitable solvent, e.g., water or a water and a water-miscible nonionic organic solvent, such resulting in physisorption (salt formation). A problem with the multilayered elements disclosed in this patent, however, is that such are not ordered. The invention disclosed is believed also to require flat substrates that have been pretreated for adsorption.
Further, there is disclosed a structure comprising ultrathin organic films in "Assembly of Polyelectrolyte Molecular Films onto Plasma-Treated Glass," J. Phys. Chem. 1993, 97, 12835-12841. One of the investigators disclosed in that article is named as a coinventor in U.S. Pat. No. 5,208,111. This article discloses a self assembly technique for constructing heterostructure films. Such multilayered assemblies are obtained by consecutive alternating adsorption of anionic and cationic polyelectrolytes from aqueous solution onto a charged substrate. The charged substrate is a glass substrate which has been treated by low temperature plasma (glow discharge) to build up a surface charge density required for the self assembly process. According to the investigators, the thickness of the multilayered film structure increases linearly with the number of layers. Further, it is disclosed that the thickness of each layer and the total thickness of the layered structure can be adjusted precisely by changing the ionic strength of the solution from which the polyions are adsorbed. According to the investigators the combination of methane plasma treatment and polyelectrolyte assembly opens a new approach for constructing inorganic/organic nanocomposite films. Nevertheless, the article does not disclose any inorganic/organic films. Also, there is no disclosure of any order within the adsorbed films.
Other technologies for the formation of multilayered structures include vacuum evaporation, sputtering, chemical vapor deposition, and atomic layer epitaxy. These methods are costly, however, in that they require sophisticated instrumentation. Further, using these methods it is difficult to incorporate intact complex molecules of interest.
Accordingly, there is still a need for multilayer elements or structures having a support on which are deposited a plurality of ultrathin layers of material not having the problems now found with multilayer structures, and their method of manufacture.